352 



ANATOMY OF VERTEBRATES. 



most characteristic feature of the organisation of the electric 

 battery is its enormous supply of nervous matter. Each organ 

 derives this supply from one branch of the trigeminal, fig. 231, a, 

 and from four branches of the vagal nerves, ib., b, C, d ; the four 

 anterior nerves are each as thick as the spinal cord : the last 

 nerve is a feeble branch of the vagus. The trigeminal and 

 vagal enlargements of the olivary and restiform tracts coalesce on 

 each side, forming the so-called 'electric lobes' of the medulla 

 oblongata. The electric branch of the fifth nerve may be defined 

 even at its origin, from the true ganglionic part of that nerve ; 

 and both this and the vagal branches consist entirely of the pri- 

 mitive nerve-fibres of animal life, as in fig. 164. The nerve- 

 trunks are distributed by successive resolution into smaller and 

 smaller fasciculi, until they finally penetrate the septa of the 

 columns, and terminate thereon by meshes formed by loops, or by 

 the return and anastomosis of the primitive nerve-fibres. 1 



In the eel-like Gymnotus the electric organs are four in 

 number, and are situated two on each side the body, extending 

 from behind the pectoral fins to near the end of the tail, fig. 232, 



232 



Right electrical orgaris, Gymnotus (reduced), ccxvn. 



k, L They occupy and almost constitute the whole lower hah of 

 the trunk, fig. 233 ; the upper organ, ib. h, being much larger than 

 the lower one, ib. i, from which it is separated by a thin muscular 

 and aponeurotic stratum. The organs of one side are separated 

 from those of the other, above by the vertebral column and its 

 muscles, ib. c, then by the air-bladder, ib. d, and below this by 

 an aponeurotic septum, ib. k. From this septum, and from that 

 covering the air-bladder, there extend outward, to be attached to 

 the skin, a series of horizontal, or nearly horizontal, membranes, 

 arranged in the longitudinal axis of the body nearly parallel to 

 one another ; they are of great but varying length, some being 

 co-extensive with the whole organ, fig. 232, k : their breadth is 

 almost that of the semidiameter of the plane of the body in 



1 I.XXVI. 



